The present invention relates to a dynamic vibration absorber capable of suppressing vibrations in horizontal two-dimensional directions of a target or object structure.
Generally, a dynamic vibration absorber includes an additional weight portion which is subjected to a force of inertia by vibrations, a rigidity element for generating a reaction force to the inertia force applied to the additional weight portion and a damping element for absorbing vibration energy.
A conventional dynamic vibration absorber is constructed such that vibrations in a specified direction of a target structure are suppressed by vibrating an additional weight portion. Hence, if there are a plurality of directions in which vibrations are to be controlled, the vibration controlling equipment must contain the same number of dynamic vibration absorbers as that of directions of vibrations.
One example of the conventional dynamic vibration absorber will be described with reference to FIGS. 10A and 10B.
In FIGS. 10A and 10B, a target structure 200 placed on a floor 201 has two vibration directions of the x- and y-axis. On the target structure 200 are placed two dynamic vibration absorbers 202a and 202b corresponding to the directions of vibrations. Each of the dynamic vibration absorbers 202a and 202b is locked to a locking structure 203a (203b). In each of the dynamic vibration absorbers, an additional weight portion 204a (204b) is supported by both a rigidity element 205a (205b) and a damping element 206a (206b).
In each of the dynamic vibration absorbers 202a and 202b, when vibrations are generated in the target structure 200, the damping elements 206a)and 206b) reduce vibration energy while the rigidity elements 205a and 205b apply reaction forces to the force of inertia generated in the additional weight portions 204a and 204b. Thus, the dynamic vibration absorbers 202a and 202b provide the damping effect for the vibrations in the x- and y-axis directions shown in FIG. 10B, respectively. In other words, in the conventional dynamic vibration absorbers, the single dynamic vibration absorber is provided to supress vibrations in one direction, that is, one for the horizontal (x-axis)direction and the other for the vertical (y-axis) direction as shown in FIG. 10B.
In the conventional dynamic vibration absorbers of the structures described above, there is no problem in a case where there is a large space for installation of the dynamic vibration absorbers and a plurality of dynamic vibration absorbers can be hence provided in a large target structure, such as a building. However, where there is a limitation to the installation space for dynamic vibration absorbers and where damping in a plurality of directions is required, as in a machinery, it is difficult to adequately install the vibration controlling devices having a conventional structure in which the directions of vibrations of the additional weight portions are determined.